Gallium metal contact switch



7 Feb. 13, 1968 E. LANGBERG ET 3,369,094

GALLIUM METAL CONTACT SWITCH 3 Sheets-Sheet 1 Filed July 15, 1966 INVENTORS LOUIS vv. ROBERTS EDWTN LANGBERG ROBERT L. SLATER, JR.

ATTORNEY Feb. 13, 1968 E. LANGBERG ET AL 3,369,094

GALLIUM METAL CONTACT SWITCH 5 Sheets-Sheet 2 Filed July 15, 1966 S R B W R m E E N B E0 N W W Sm uW O D L E ROBERT L. SLATE R, JR.

ATTORNEY Feb. 13, 1968 LANGBERG ET AL 3,369,094

GALLIUM METAL CONTACT SWITCH Filed July 15, 1966 3 Sheets-Sheet f INVENTORS ,LOUIS W. ROBERTS EDWTN LANGBERG BY ROBERT L. SLATER, JR.

AT TORNEY 3,369,094 GALLIUM METAL CONTACT SWITCH Edwin Langberg, Lexington, and Louis W. Roberts, Wakefield, Mass., assignors to Metcom, Inc., Salem, Mass., a corporation of Delaware Filed July 15, 1966, Ser. No. 565,449 10 Claims. (Cl. 200-140) ABSTRACT OF THE DISCLOSURE A high voltage of large current capacity having a first electrode spaced from a second electrode with a liquid metal disposed therebetween. An electrical connection is made when the electrodes contact the liquid metal and the electric-a1 connection is broken when one electrode is moved out of contact with the liquid metal.

This invention relates to electrical switching devices. More particularly, it pertains to an improved arc-suppression liquid metal switch.

At the instant of interruption of high voltage, when the separation distances between the switch electrodes are 10- cm. or less, an electric field of very large magnitude is created. The switch cathode, whether it be a solid or liquid metal electrode, emits some quantity of ionized metal vapor along with substantial thermionic and field emission electron flow sufiicient to initiate arcing. The resultant ionized metal vapor cools and condenses on the interior surfaces of the switch. When sufiicient metal vapor film has collected on the dielectric parts of a switch, undesired current leakage or even shorting of the switch may occur. Thus, the vapor-forming characteristics of the electrode material are import-ant to the selection and design of a switch for the interruption of high voltage.

Further, while self-healing liquid metal electrodes have many advantages over solid metal electrodes in high voltage interruption devices, the advantages have been ofiset by the more intense vaporization of the liquid metal electrodes compared to that of solid electrodes and, in some applications, by severe splattering of the liquid metal electrode materials during switch arcing. Liquid metal droplets splattered about the interior of a high voltage switch quickly add to the vaporized metal deposits on dielectric parts of the switch, hastening current leakage and switch shorting.

It should be noted that while mercury is commonly used in room light switches, thermostats, and other low voltage devices, it cannot be used in high voltage devices because of its unfavorably high vapor pressure at room or elevated temperatures. However, an electrode material which is suitable for high voltage devices is gallium and certain of its alloys.

At normal atmospheric pressure, gallium metal is liquid between 30 C. and 2403 C. Even at 10* torr pressure, gallium does not vaporize below 742 C. Eutectic alloys of gallium, prepared with indium and tin, exhibit melting points as low as C. and do not have significantly increased vapor pressure over that of pure gallium. Gallium metal has roughly twice the conductivity of mercury. Moreover, liquid gallium does not significantly attack commonly used electrode materials. Tungsten and graphite are in fact substantially free from corrosive chemical reactions with liquid gallium. Thus, gallium metal in the liquid state is a superior electrode contact matcral.

Heretofore, liquid metals, including gallium, have not been successfully employed in interrupting high voltage power mains, notwithstanding the considerable advantages of self-healing electrodes so formed, due in part to the absence of a satisfactory means to negate the effects of arc-splattered liquid metal and to suppress undesired metal vapor deposits on switch dielectric parts.

States Patent 0 3,3b9,94 Patented Feb. 13, 1968 ice It is, therefore, an object of this invention to provide a novel high voltage switch of large current capacity using a liquid metal electrode contact.

Another object of this invention is to provide a novel liquid metal electrode switch contact.

Another object of this invention is to provide a high voltage switch with little tendency to are utilizing a liquid gallium metal contact.

Still another object of this invention is to provide a novel high voltage switch of large current capacity utilizing a liquid gallium metal electrode contact.

Yet another object of our invention is to provide a novel liquid metal electrode switch contact which suppresses the side effects of metal vapor deposition and of liquid metal splattering within the interior of the switch.

These and other objects and advantages of our invention will be apparent from the following drawings, specification and claims.

FIGURE 1 is a cross-section view of a first preferred embodiment of our invention.

FIGURE 2 is a cross-section view of a variation in the preferred embodiment of our invention shown in FIG- URE 1.

FIGURE 3 is a cross-section view of a second embodiment of our invention.

FIGURE 4 is a cross-section view of the embodiment of our invention shown in FIGURE 3, viewed from a plane shown at 44 in the illustrations.

FIGURE 5 is a partially cut away view of still another embodiment of the concept of our invention.

Referring now to the drawings, FIGURE 1 illustrates a first preferred embodiment of our invention comprising a high strength dielectric envelope 10, a fixed electrode 12 mounted within the envelope 10, and a movable electrode 14 slidably mounted within a spaced distance relationship to the first electrode 12. Electrical contact between the electrodes. is made through a quantity of liquid gallium metal 16 positioned within the space between the electrodes and is retained therein by reason of the electrode configurations described below.

An envelope 10 shown in the embodiment of FIGURE 1 is comprised of a cylinder 20 of high dielectric strength, sealed at the lower end with a metallic flanged end plate 22. The end plate 22 is joined about the outer perimeter 24 to the dielectric cylinder 20; and through a flared central aperture 26, it is rigidly mounted to the electrode 12. The second end of the cylinder 20 is similarly sealed about the movable electrode 14 by means of a flanged end plate 30 having a central aperture 32, the flared perimeter of which is integrally mounted to the movable electrode 12. A cylindrical metal bellows 36 is mounted to the outer perimeter 34 of the end plate 30. The bellows 36, of about the same diameter as the dielectric cylinder 20, is sealed, as shown in the drawings at 38, about the edges of the dielectric cylinder 20. The bellows 36 is adapted to axially expand or contract, in response, respectively, to axial tension or compression. The axial movement provided by the bellows 36 is sufficient to separate or to make electrical contact between the electrodes 12 and 14, in directions A and B respectively, but is limited by the cylindrical bracket 40 mounted to cylinder 20.

The electrode 12 is rigidly attached by metallurgical bonding to the end plate 22 and is, accordingly, a fixed electrode. The liquid gallium metal is retained within concave recess 42 which is positioned centrally within the interior of the electrode 12. The recess 42 is shaped to provide ample space through which the movable electrode 14 passes to make contact with the liquid gallium 16 at the lowermost portion of the recess 42. Electrical contact between the electrodes 12 and 14 is effected through a quantity of liquid gallium 16.

The movable electrode 14 is elongated. It is rigidly attached to the end plate 30, which in turn is subject to movement through axial contraction and expansion of the bellows 36. The extreme end 44 of the electrode 14 is convex and is shown conically shaped to conform to the contour of the recess 42, which is shown concave conical in this embodiment. Relatively small axial movement of the electrode 14 with respect to electrode 12 alters the total surface-to-volume ratio of the volume in which the gallium metal 16 is deposited. Hence, the surface areas of the two electrodes 12 and 14 are exposed to substantially equal areas of contact with the gallium metal 16. This assures substantially equal electrode current heating and electrode current density.

Since small axial movements of the electrodes 12 and 14 with respect to one another will rapidly alter the surface area of the two electrodes exposed to contact with the liquid gallium metal once electrical contact is initiated, a minimal period of time is required to expand electrode contact and to effect reduction of the current con-centration and resultant extreme electrode heating. Conversely, separation of the electrode surfaces from the liquid gallium metal is accelerated as the gallium metal flows downward into the expanding free volume of the recess 42.

Thus, by means of the complementary shaping of the two electrodes 12 and 14 and by the use of an intermediate liquid metal contact, a significantly low switching time is achieved. Also, arcing is thereby minimized.

It should be noted that gallium requires a heat of vaporization comparable to that required by silver or copper and several times that required by mercury. Thus, the gallium switch will arc for a short time, comparable to the arcing time of a silver or copper switch and with a comparable power loss. In this regard it will perform substantially better than a mercury switch.

Electrode 12 is provided with a cylindrical flange 48 which extends well upward and beyond the recess 42. Liquid gallium metal which is splattered during switching action is caught on the interior surfaces of the flange 48 and returned by gravitational flow back to the recess 42.

Electrode 14 is provided with an insulating sheath 50 which extends axially along the electrode sides but not over the electrode end 44. The outer diameter of insulating sheath 50 is less than the inner diameter of the cylindrical flange 48. The space separating the sheath 50 and flange 48 is narrow to prevent splattered liquid metal from escaping from the electrode 12 interior recess 42 but is sufficiently large to allow axial movement therebetween. Liquid metal splattered onto the surfaces of the insulating sheath 50 is returned by gravitational drainage back along the electrode 14 and into the recess 42. A cylindrical bracket 40 limits the axial movement of electrode 14 with respect to electrode 12 in order that no excess movement thereof in the direction B can be made which will tend to express the liquid gallium metal 16 from the recess 42 at 52.

The proper configuration of the insulating sheath 50 and the flange 48 prevents short circuiting of the electrodes 12 and 14 and prevents liquid gallium from splattering the envelope or the electrode 14, which short circuiting could otherwise have been possible due to the wetting properties of gallium.

Envelope 10 is evacuated to minimize ionization of gas particles in the interelectrode space 54, which ionization has been observed to be a function of the pressure of the gas times its density (Paschens law). At pressures below 10" torr, there will remain only a negligible number of gas particles from the surroundings. An electric field of the order of 10 kv./cm. can be applied to this switch without any breakdown due to field emission.

Since at the vapor pressure of 10- torr the vaporization temperature of gallium is approximately 742 C., gallium is well suited for high vacuum switching. The work function of gallium is approximately 4.12 ev., at

temperatures even up to 800 C.; accordingly, there will be negligible thermionic emission.

In the embodiment of our invention illustrated in FIGURE 2, element is an envelope of high dielectric strength. A first electrode 112 is mounted to the envelope 110. A second electrode 114 is also mounted to the envelope 110, within a fixed spatial relationship to electrode 112. A movable electrode 116 is slidably mounted between electrodes 112 and 114 so that, at the lower extremity of its motion, electrode 116 rests snugly against electrode 112 and, at the upper extremity of its motion, electrode 116 rests in close spatial proximity to electrode 114. Electrical contact is accomplished from electrode 112 to electrode 116 by the sliding contact at 118, and from electrode 114 to electrode 116 through a quantity of liquid gallium metal 120, which gallium is positioned within the spaced distance between the electrodes 114 and 116 and retained thereat by reason of the electrode configurations described below.

Envelope 110 consists of a cylinder 122 of high dielectric strength sealed to lower cover 124 about the outer perimeter 126 thereof. Electrode 112 is inserted through a flared central aperture 128 of the lower cover 124 and is there sealed to lower cover 124. Cylinder 122 is similarly sealed to upper cover "130. Electrode 114 is similarly inserted through a flared central aperture 132 of upper cover and is there sealed to upper cover 130.

Cylindrical metal bellows 134, self-enclosed at the lower end 136, is mounted to electrode 112 at the perimeter of the upper open end 138. Through the internal surface of the lower end 136 of bellows 134 is integrally mounted impeller -140. Impeller 140 is integrally mounted to electrode 116 through an appropriate aperture 142 in electrode 112, making no electrical contact with electrode 112.

Through the external surface of the lower end 136 of bellows 134 is integrally mounted the extrusion of impeller 140 which is movable by an external mover in the directions K and L. Movement of impeller 140 and the elements integrated thereto in the direction L is at the extremity at the position where electrode 116 has come to rest against electrode 112. Means 144 is provided to limit motion thereof in the direction K. Bellows 134 is adapted to axially expand or contract in response, respectively, to tension or compression.

The configuration of electrode 116 includes a concave recess 146 within which is retained the quantity of liquid gallium metal 120'. The axial movement provided by the bellows 134 is sufficient to separate or to make electrical contact between the electrodes 114 and 116 through the liquid gallium metal 120. The extreme end 148 of electrode 114 is convex and is shown comically shaped to conform to the contour of the recess 146, which is shown concave conical in this embodiment. Relatively small axial movement of the electrode 116 with respect to electrode 114 alters the total surface-to-volume ratio of the volume in which the gallium metal 120 is deposited. Hence, the surface areas of the two electrodes are exposed to substantially equal areas of contact with the gallium metal 120. This assures substantially equal electrode current heating and electrode current density.

Since small axial movements of the electrodes 114 and 116 with respect to oneanother will rapidly alter the surface area of the two electrodes exposed to contact with the liquid gallium metal once electrical contact is initiated, a minimal period of time is required to expand electrode contact and to efiect reduction of the current concentration and resultant extreme electrode heating. Conversely, separation of the electrode surfaces from the liquid gallium metal is accelerated as the gallium metal flows downward into the expanding force volume of the recess.

Thus, by means of the complementary shaping of the two electrodes 1'14 and 116 and by the use of an intermediate liquid metal contact, a significantly low switching time is achieved. Also, arcing is thereby minimized. The previous discussion of arcing is applicable here.

Means 144 limits axial movement of electrode 116 in the direction K in order that no excessive movement thereof in the direction K can be made which would tend to express the liquid gallium metal 120 from the recess 146 at 150.

Electrode 116 is provided with a cylindrical flange 152 which extends well upward and beyond the recess 146. Liquid gallium metal which is splattered during switching action is caught on the interior surfaces of flange 152 and returned by gravitational flow back to the recess 146.

Electrode 114 is provided with an insulating sheath 154, which extends axially along part of the electrode sides but not over the electrode end 148. The outer diameter of insulating sheath 154 is less than the inner diameter of the cylindrical flange 152. The space chosen to sepa rate the sheath 154 and flange 152 is narrow and prevents splattered liquid metal from escaping from the interior recess 146 of electrode 116, but it is sufficiently large to allow axial movement therebetween. Liquid metal splattered onto the surfaces of the insulating sheath 154 is returned by gravitational drainage back along the electrode 114 and into the recess 14'6.

The surface contact 118 between electrode 112 and electrode 116 is wetted with liquid gallium metal which serves to insure electrical contact therebetween and to lubricate the sliding elements.

Envelope 110 is evacuated. The discussion of the effect of evacuation and of related matters, made in the description of the first preferred embodiment, is here applicable.

In the embodiment of our invention illustrated in FIGURES 3 and 4, element 210 is an envelope of high dielectric strength. A first electrode 212 is mounted to the envelope 210. A second electrode 214 is rotatably mounted to the envelope 210. The configuration of electrode 214 is eccentric so that, at certain angles of its rotation, electrode 214 is positioned close to electrode 212 and, at other angles of its rotation, electrode 214 is positioned far from electrode 212, relative to the close position. Electrical contact is accomplished between electrode 212 and electrode 214 through a quantity of gallium metal 220 positioned within the spaced distance between electrodes 212 and 214 and retained there by reason of the electrode configuration described below.

Envelope 210 consists of an oblong container 216 enclosed on five sides. The sixth side of the container 216 is formed by plate 218, sealed to container 216 at the outer periphery 222 of plate 218. Electrode 212 is inserted through a flanged central aperture 224 of the plate 218 and is there sealed to plate 218.

Eccentric electrode 214 is integrally mounted on a conductive axle 226 which forms an integral part thereof. Axle 226 is rotatably mounted in bushings 228 and 230, each being integrally mounted in the opposite walls of container 216. Bushing 230 is conductive. Bushing 230 extends beyond the surface of the container wall 232 in which it is mounted so as to provide a configuration whereby an outside element may be connected thereto. Electrical contact is accomplished from bushing 230 to electrode 214 through surface contact between the bushing 230 and conductive axle 226, which is an integral part of electrode 214. Electrical contact between electrode 214 and electrode 212 is accomplished through the quantity of liquid gallium metal 220 positioned in an appropriate recess 234 in electrode 212. The recess 234 is formed so as to conform to the extremity 236 of electrode 214, which is positioned close to electrode 212 at certain angles of the rotation of electrode 212. Hence, the surface areas of the two electrodes are exposed to substantially equal areas of contact with the liquid gallium metal 220. This assures substantially equal electrode heating and electrode current density.

Angular movement of electrode 214 is mechanically provided by spur gearing 238, which is arcuately positioned on a portion of eccentric electrode 214 by means of a spur gear 240 operatively mounted thereto. Means 242, mounted within envelope 210 and responsive to external control, powers spur gear 240. Suitable devices are known to the art. Spur gear 240 and the elements connected thereto are not conductive. FIGURES 3 and 4 show with dashed lines the eccentric electrode 214 approximately at one extreme of its angular motion, and, with solid lines, show the same element approximately at the other extreme of its angular motion.

Since small angular movement of the electrode 214 will rapidly alter the surface area thereof exposed to contact with the liquid gallium metal once electrical contact is initiated, a minimal period of time is required to expand this electrode contact and to effect reduction of the current concentration and resultant extreme electrode heating. Conversely, separation of the electrode surfaces from the liquid gallium metal is accelerated as the gallium metal flows downward into the recess.

Thus, by means of the complementary shaping of the two electrodes 212 and 214 and the use of the intermediate liquid metal contact 220, the switch may be operated in a significantly low switching time. Also, arcing is thereby minimized. The previous discussion of arcing is applicable here.

. Electrode 212 partially envelopes the volume in which electrode 214 rotates, at no place however making contact with electrode 214 except through the intermediate liquid gallium metal 220. The configuration of electrode 212 is such that any liquid gallium metal that is splattered during the switching process strikes one of the electrodes and flows back down to the recess 234. No liquid gallium metal can thus wet the container 216 and thereby possibly cause a short circuit.

Envelope 210 is evacuated. The discussion of the effect of evacuation and related matters made in the description of the first preferred embodiment is here applicable.

If a designed breakdown voltage is desirable, means, such as adjustment threads, can be adapted to vary the separation gap between the movable electrode and the relatively fixed electrode described in embodiments .0 this invention.

Some of the numerous advantages of our invention are now evident.

These gallium switches have all of the advantages of the liquid metal switches now known to the art; As well, the heat of vaporization of gallium, which is high compared to mercury which is used in switches known to the art, gives the advantage that less vapor from boiling of the electrode material will form from gallium than from mercury at the point of contact breaking. If the other electrode is of a material that does not vaporize readily, the resultant arcing will be minimized. I

It should be noted that gallium has excellent wetting properties on all metals, as well as on glass, quartz, and ceramics. Below C., gallium does not attack any metal significantly. Tantalum resists gallium corrosion at temperatures up to 350 C. And tungsten and graphite are not affected by gallium even at 800 C. In this regard gallium is a superior electrode material.

The properties of gallium allow the design of a reed switch for high power application. FIGURE 5 shows such a switch. Envelope 310 consists of cylinder 311 of high dielectric strength, sealed at its lower end to lower base 312, and similarly sealed to an upper base.

Electrode 313 is cantilevered to base 312. Electrode 314 is similarly cantilevered to the upper base. Electrodes 313 and 314 are essentially flat reeds of nickel-iron or other ferromagnetic material. Electrodes 3 16 and 314 are separated by a small gap when in their normal positions.

When a magnetic field N-S is applied to the electrodes 313 and 314, they assume opposite polarity, flex, and make contact. Reduction or interruption ofthe magnetic field permits electrodes 313 and 314 to return to their normal positions.

Electrode 314 is wet-ted with liquid gallium 31 5 on the surface at which contact is made to the other electrode 313. Electrode 313 is similarly wetted with gallium. This gallium-wetted contact ofiers low and consistent resistance because of the self-healing qualities of the liquid gallium.

The relatively high heat of vaporization of gallium, compared to that of mercury, results in less wetting metal being lost as vapor from the electrodes under heavy loads. Such gallium as is lost in vapor form will condense on the inside surfaces of the switch and flow down to the base 312 which thus serves as the bottom of a reservoir.

In the preferred structural embodiments of our invention which we have described, we have provided a switch within which splattered liquid metal is caught and returned to the proper depository. Since our gallium switch has minimal .arcing, due both to the properties of gallium and to the design of electrodes such that electrode separation may be rapidly performed, our gallium metal contact switch satisfactorily suppresses the formation of undesired metal vapor.

The solid-to-liquid junction is, of course, self-healing. Thus, the junction is of maximum area,-since the liquid metal makes contact with the solid electrode even where the solid electrode is pitted. Since the resistivity of liquid gallium is roughly one-third that of mercury, it should be noted that gallium is again superior to mercury.

We do not intend to limit our invention to the descriptions that we have made of specific preferred embodiments thereof. Clearly, in many applications of our gallium switch, it will be preferable to use alloys of gallium. For example, eutectic alloys of gallium and tin exhibit melting points as low as 5 C. without significantly increased vapor pressure. Alternatively, or in addition thereto, a heating element may be provided if environmental conditions are such that the switch will be in operation at a temperature less than 30 C., which is the melting point of commercial gallium. It should be noted that high purity gallium supercools very greatly and can remain liquid at much lower temperatures. Further, many variations and refinements, such as the earlier described adjustment and threads, can be made in the structural embodiment of our invention without departing from the scope of our invention.

Our invention is meant to include all technically equivalent materials and elements, as well as materials and elements that perform essentially similar functions.

Having thus described our invention and some of its advantages, we accordingly claim:

1. An improved high voltage switch of large current capacity, comprising a first and a second electrode; a concave reservoir within the first electrode, the electrodes being mounted movably with respect to one another in spaced relationship therewith the inner end of the second electrode extends deeply into the reservoir, said mova ble electrode being tapered outwardly from said inner end, the taper of the movable electrode cooperating with said concave reservoir to provide deflection surfaces for the liquid metal splattering out from the reservoir; and a quantity of liquid gallium metal in the reservoir; whereby movement of the second electrode with respect to the first electrode makes electrical contact between the electrodes through the liquid gallium metal when the second electrode is inserted deeply into the quantity of gallium metal in the reservoir, and electrical contact between the electrodes is broken when the second electrode is partially withdrawn from the reservoir.

2. A high voltage switch of large current capacity, comprising a high dielectric strength evacuated envelope; a first and a second electrode, the electrodes being mounted within the envelope and in movable spaced relationship of one to the other; separate means for making electrical contact exterior of the envelope with each electrode; a deep concave reservoir within the first electrode; a quantity of liquid gallium metal contained within the reservoir, the inner end of the second electrode being mounted to extend deeply into the reservoir and to partially withdraw from the reservoir upon movement; whereby movement of the second electrode with respect to the first electrode makes electrical contact between the electrodes through the gallium metal when the second electrode is inserted deeply into the quantity of gallium metal in the reservoir, and electrical contact is broken when the second electrode is partially withdrawn front the reservoir and means for varying the current substan-" tially equal in each of said electrodes.

3. An improved high voltage switch of large current capacity, comprising a high dielectric strength evacuated envelope; a first electrode mounted within and extending through the envelope; a second electrode movably mounted within the envelope in a spaced distance relationship to the first electrode; a deep concave reservoir within the second electrode; and a quantity of liquid gallium metal within the reservoir, the first electrode extending deeply into the reservoir and the second electrode mounted to move the surface of the gallium metal into and out of contact with the first electrode; whereby electrical contact is respectively made and broken between the electrodes, said first electrode tapering outwardly to cooperate with the concave reservoir to provide deflecting surfaces for said liquid metal.

4. An improved high voltage switch of large current capacity, comprising a first and a second electrode, the first electrode being fixedly mounted and the second electrode being movably mounted within a spaced distance with respect to the first electrode; a concave reservoir within the first electrode, a portion of the second electrode extending into the reservoir and adapted to move a spaced distance within the reservoir; and a quantity of liquid gallium metal in the reservoir; whereby the spaced distance movement of the second electrode alternately places the second electrode within and without the liquid gallium metal, thereby respectively making and breaking electrical contact between the electrodes the surface of said recess being formed substantially concave-conical and the outside surface of said movable electrode being formed substantially convex-conical to conform to the concave contour of said recess, the quantity of said liquid metal cooperating with said concave and convex surfaces whereby the areas of contact of said surfaces with said liquid metal are substantially equal for variations in the position within a predetermined distance inside the liquid metal of the second electrode with respect to the first electrode and thereby maintaining substantially equal current in each said electrode.

5. An improved high voltage switch of large current capacity, comprising an electrically insulating evacuated member having a concavity; a first and a second electrode mounted in spaced relationship within the concavity; a deep reservoir within the first electrode; and a quantity of liquid gallium metal within the reservoir, the second electrode eccentrically mounted in a rotatable spaced relationship to the first electrode in the reservoir; whereby electrical contact between the electrodes is made through the liquid gallium metal when the eccentric electrode is rotated into contact with the gallium metal, and electrical contact is broken when the eccentric electrode is rotated out of contact with the gallium metal.

6. An improved, rapidly actuated, high voltage reed switch, comprising a first electrode and a second electrode, the electrodes having a coating of liquid metallic gallium applied thereto; a gas tight, evacuated envelope, the two electrodes being cantilever mounted within the envelope in parallel spaced relationship a magnetic means having an on and off condition is associated with the first and second electrodes, said magnetic means being positioned to cause said electrodes to bow outwardly whereby the outer end of each electrode contacts the other electrode when the magnetic means is on, said electrodes returning to said parallel relationship when the magnetic means is off, the two electrodes thereby making electrical contact through a lubricating film of liquid metallic gallium; whereby the region of electrode contact is at all times lubricated and impact welding of the electrodes is eliminated.

7. The high voltage switch of claim 1, wherein said inner end of the movable electrode is substantially conically shaped and substantially complementary with said concave reservoir.

8. The high voltage switch of claim 7 wherein a cylindrical flange is secured to said first electrode and extends upward therefrom, said cylindrical flange providing a deflecting surface tfOI said liquid metal, said movable electrode extending Within the cylindrical flange; and

an insulating sheath extends around said movable electrode to prevent short circuiting of the first and second electrodes from the splatterings of said liquid metal.

9. The high voltage switch of claim 2 wherein said means for varying the current substantially equal comprises the surface of said recess being substantially concave-conical and the outside surface of said movable electrodes being formed substantially convex-conical toconform to the contour of said recess, the quantity of said liquid metal cooperating 'with said concave and convex surfaces whereby the areas of contact of said sunfaces with said liquid metal are substantially equal for variations in the positionwithin a predetermined distance in- 10 side the liquid metal of the second electrode with respect to said first electrode.

10. The high voltage switch of claim 3, wherein a third electrode is mounted to said envelope, said second electrode having a first position whereby said second electrode electrically contacts said third electrode and said liquid metal is out of contact with said first electrode, said second electrode having a second position whereby said second electrode is out of contact with the third electrode and the liquid metal is in contact with said first electrode.

References Cited UNITED STATES PATENTS BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner. 

